Seasonal affective disorder (SAD)

Seasonal affective disorder (SAD) is the feeling of depression during the winter months. For people with SAD, these episodes of depression will recur at the same time each year.

  1. Symptoms include low mood and lacking interest in life
  2. One of the main causes is lack of sunlight
  3. Sometimes treated with CBT and antidepressants

SAD is classed as a form of depression. It can be a disabling condition that requires hospital admission, if the symptoms are particularly severe. If you would like to speak to a doctor about SAD and what treatment options are available our online video consultation service may be able to help.

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Seasonal affective disorder is a form of depression that occurs regularly for two or more years during the winter months. Symptoms gradually get worse during autumn, followed by a remission of symptoms during spring and summer. 

There is no specific cause for SAD, but there are thought to be a number of risk factors. There is a higher incidence rate for those who have first-degree relatives with the condition, suggesting that there may be a genetic link. Living somewhere with diminished light during the winter, combined with particularly sunny exposure during the summer, is also a risk factor. Women are between three and five times more likely to develop SAD than men, and it’s more common among people aged 20 to 30. 

An internal ‘clock’, or circadian rhythm, is responsible for regulating hormone release in our bodies. These help to manage our functions, telling us when to be awake and alert, and when to relax. When the days become shorter, and we spend more time in darkness, this can disrupt the hormonal pattern.

For example, reduced exposure to sunlight can affect melatonin levels, which regulate how awake we are. Serotonin levels are also much lower for people with SAD during the winter months. Sunlight helps to stimulate the function of the hypothalamus, a part of the brain that regulates physiological cycles and emotional responses.

Around 2% of Northern Europe are thought to have some form of SAD. In the UK, 6% of the adult population have recurrent major depressive episodes. It is thought that four out of 10 people with SAD also have other minor depressive symptoms at some point throughout the year.

SAD doesn’t always require treatment. Self-help measures, such as getting more sunlight during the daytime, and exercising regularly, can help to alleviate symptoms.

When treatment for SAD is recommended, it’s normally treated in the same way as depression - through cognitive behavioural therapy, and sometimes with medications such as SSRIs. Light therapy is another option someone might consider, although there is little evidence at present to confirm how effective this is.

SAD can be a particularly challenging condition if depression during an episode is severe, but our doctors may be able to help. They can provide advice on how to reduce symptoms and recommend treatment where needed. You can book an appointment to speak to one of our UK doctors at a time that suits you best.

Page last reviewed:  24/02/2020
Diagnosis and treatment

How does someone know they have seasonal affective disorder?

There are several factors that someone may consider to assess whether they could have seasonal affective disorder (SAD). 

The onset of a lowered mood will happen at a particular time in the year that is not otherwise influenced by other possible stressors. The symptoms of depression will also resolve themselves during the spring, and through the summer. 

As well as affecting your mood, SAD can have an effect on eating and sleeping patterns. It is likely to make you feel more lethargic and less active.

It can often be difficult to know whether you have SAD. Due to the nature of the condition, you may have to observe symptoms over a period of two or more years for the pattern to become clear.

How is SAD diagnosed?

The four signs that a doctor will use to diagnose SAD are:

  • A clear relationship between the time of year and the onset of depressive symptoms
  • A remission of symptoms during spring and summer
  • At least two episodes of major depression over two years occurring during the same period of time each year
  • More episodes of seasonal depression than non-seasonal.

They will use the above criteria in addition to screening for the symptoms of depression.

Does seasonal affective disorder require treatment?

Not always. Lifestyle measures, such as getting more sunlight, exercising outdoors and eating a healthy and balanced diet can help to improve symptoms. 

Where this doesn’t work, cognitive behavioural therapy (CBT) or antidepressant medication (or both) may be used (as they are in depression).

What treatments are there for seasonal affective disorder?

It is recommended by NICE guidelines that SAD is treated in the same way as depression. This means that a combination of CBT, or other psychotherapies and antidepressants, may be used.

CBT involves changing the way you react to situations, through either group or individual sessions, or self-help measures. A specialist will hold sessions with a patient or group over the course of several weeks or months. 

Selective serotonin reuptake inhibitors (SSRIs) are the preferred antidepressants for treating SAD. They can take up to six weeks to take effect.

Page last reviewed:  24/02/2020
Questions and Answers

What should I do if I think I might have seasonal affective disorder?

If you have symptoms of depression during the winter months that subside around springtime, you may have SAD. You should contact your local GP if this is the case. They will be able to recommend measures you can take to try and alleviate symptoms, and refer you to a specialist for cognitive behavioural therapy (CBT) where needed.

Are there side effects of seasonal affective disorder treatment?

It depends on the treatment.

Light therapy can sometimes lead to headaches and nausea, but this can be avoided by not exposing yourself to the light for more than 30 minutes. 

SSRIs can have side effects depending on the individual. These may include a reduced sex drive, an increased appetite and general feelings of lethargy.

Can I consult a doctor about seasonal affective disorder online?

Yes. If you would like to speak to a doctor online about SAD, you can use our private video consultation service. They can refer you to a specialist for CBT, or prescribe SSRIs if you are already taking them on the advice of a doctor. You can book an appointment at a time convenient for you.

Page last reviewed:  24/02/2020

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